Utterly no problem whatsoever power-wise. It will blow-away Unity and is a great machine for it.

HOWEVER...

Note that --

Realistically to enjoy using Unity you need three, or at least two, 27" monitors.

It's not totally clear if you can chain two of these http://www.apple.com/displays/

on to the new MacBook Air -- I believe possibly NOT.

No problem on a MBP it seems ..

This is a strong argument to just buy an ordinary 27 iMac instead.

Unity is not a very portable experience - when you're in your house you'll never use it without another monitor plugged-in.

(On a related note, IMO, the retina screen laptops are problematic for Unity. The guys at Unity have a thing where they only believe in incredibly, staggeringly small font sizes, and you can't change it. (I literally keep a magnifying glass on hand to work!!)

A good thing about those new models is, apple, has finally changed to hot-rod SSD chips, instead of the " ' slow ' " SSD chips they have used the last few years. So that saves you doing an "immediate upgrade on purchase".

All of this happily brings us to the most amazing thing that has ever been in the universe .. the coming new "nuclear power plant cooling tower" power Mac .. OMG. Let us at them! :O